An atomic force microscope is a device capable of imaging samples at the nanoscale level. The atomic force microscope typically includes a cantilever that has an extremely small radius of curvature. A tip extends from the cantilever and may be placed into contact with a sample being examined or may be spaced from the sample depending upon the specific testing scheme. In contact mode, the tip is placed against the sample and drug across its outer surface. A laser is reflected off of a portion of the top of the cantilever usually opposite the tip. The reflected laser light is then directed onto an array of photodiodes. Stimulation of different photodiodes results in data that can be processed to develop a three dimensional image of the surface of the sample.
As stated, atomic force microscopes are also arranged so that the tip extending from the cantilever is positioned some distance from the sample. Here, an electron cloud circling the tip interacts with an electron cloud at the surface of the sample to cause the tip to be repelled. The cantilever can be externally oscillated at a known phase, frequency and amplitude. Certain systems focus a laser onto the tip in order to generate these known parameters. The interaction between the surface and the tip will cause the phase, frequency and amplitude of the cantilever to be different than that at which it was originally motivated. These differences can be measured and yield information about various characteristics of the sample. Atomic force microscopes are capable of measuring contact forces, electrostatic forces and magnetic forces of the sample and can also provide topographic data as previously indicated.
Chemical bonds which make up the surface of the sample vibrate at different energy levels depending upon the shape of their molecular surfaces, their mass, and the type of exhibited coupling. Infrared light applied to the surface will be absorbed at different wavelengths depending upon the arrangement of bonds present. Multiple wavelengths of infrared light can be measured through use of a Fourier transform to create a graph of wavelength absorption. From this information the types of bonds present may be deduced to then result in an identification of the chemical composition of the surface.
Atomic force microscopes are also arranged to provide data regarding both topography and thermal conductivity of a sample. For example, one such atomic force microscope employs a tip that is a thermal resistor. Current is passed through the tip as it is moved over the sample. The amount of current needed to maintain the tip at a constant temperature is measured to result in a thermal conductivity map of the surface of the sample. At the same time, the topography of the surface can be measured so that this data is acquired in addition to the calorimetric properties.
Although various atomic force microscopes are known for acquiring different types of data from samples, prior atomic force microscopes are limited in that a particular system cannot provide certain combinations of data. Accordingly, there remains room for variation and improvement within the art.